1. Field of the Invention
The present invention relates to apparatus and a method for inspecting the surface of an object.
2. Discussion of the Prior Art
Product surface inspection procedures are widely used in various industries. One such industry where careful surface inspection is essential is nuclear fuel production. Typically, nuclear fuel pellets are produced to high quality standards and after inspection following manufacture are loaded into tubes known as fuel rods or pins which are assembled together and in due course and loaded for use in a nuclear reactor. It is a customer requirement that inspection of all fuel pellets is carried out before loading into pins. This reduces the possibility of defective pellets causing pin damage when the pin is subject to high temperature and pressure in use.
At present, it is conventional for trained inspectors to perform nuclear fuel pellet inspections with the pellets held on trays. This manual inspection procedure has a number of disadvantages, viz:
(a) the standard of inspection is variable dependent upon the subjective judgement of the individual inspector, and is open to operator error; PA1 (b) the inspector has to be close to the pellets; where the fuel pellets comprise MOX (mixed oxide) fuel pellets, eg comprising mixtures of uranium and plutonium oxides, this may be unacceptable from a safety point of view; PA1 (c) the time and cost of the human work required to carry out the inspections is substantial.
Optical techniques for automatically inspecting objects such as nuclear fuel pellets are known in the prior art. For example, Applicants' prior EP 0 583 092 A1 describes such a technique using reflection of a laser beam spot by the inspected object.
One major problem which the known techniques using reflection of light are not capable of solving is that different surface flaw and defect types can reflect light in similar ways and this means that information about the defect or flaw provided by the reflected light may be limited. In some cases it may be difficult for the detection system to differentiate between different defect and flaw types or normal variation in surface appearance and flaws.